High expression of PRL-3 had been implicated in lymph node metastasis of gastric cancer. In the present study, we detected the expression of PRL-3 in primary gastric cancer tissue, and evaluated its role in gastric cancer growth and the prognostic impact on patients. PRL-3 phosphatase expression was measured in 137 gastric tumor samples by using the immunohistochemistry method, and the overall survival rate was compared between the patients with high PRL-3 expression (n = 85) and those with moderate or low PRL-3 expression (n = 52). RNA interference, mediated by recombinant lentivirus expressing artificial PRL-3 miRNA, was used to knockdown PRL-3 expression in SGC7901 cell line. MTT assay and animal experiment were conducted to determine the role of PRL-3 in the proliferation of SGC7901 cells and tumor growth. PRL-3 expression was more frequently detected in tumors with a diameter >40 mm and in advanced stages. Furthermore, the overall survival rate of high PRL-3 expression was significantly lower than that of moderate or low PRL-3 expression (P < 0.001), and multivariate analysis showed that PRL-3 expression level independently influences the survival of patients (P = 0.024). Importantly, knockdown of PRL-3 significantly suppressed the proliferation of SGC7901 cells and slowed the tumor growth compared with controls (P < 0.05). PRL-3 is associated with gastric cancer progression. High PRL-3 expression in the primary lesion had a negative impact on prognosis. PRL-3 plays a key role in the control of gastric cancer growth. PRL-3 should be considered as a potential therapeutic target and a prognostic factor.